Prachi Mehndiratta, MBBS

Intracerebral hemorrhage like other structural brain lesions is known to cause disruption of the blood brain barrier (BBB) and extravasation of fluid into the surrounding tissue. Stroke neurologists refer to this seepage of fluid from the intravascular to the extravascular space as vasogenic edema. The permeability of the BBB can be determined by determining the extent of contrast extravasation during CT perfusion (CTP) scans. The authors of this study proposed that the rate of iodinated contrast extravasation a.k.a. Permeability Surface area product (PS) that serves as an estimate of BBB permeability is increased in the peri-hematomal region and is predictive of hematoma growth.

The authors studied patients previously enrolled in the ICH ADAPT study (a prospective, randomized clinical trial evaluating the effect of BP reduction on cerebral blood flow (clinicaltrials.govNCT00963976)). All patients underwent non-contrast CT scans at baseline, 2±1h and 24±3h post-randomization and CTP imaging was performed at 2h. Post processing of images was performed to identify regions of interest and calculate hematoma volume; perihematoma edema volume and PS maps were generated. Out of 75 patients enrolled in ICH ADAPT, 53 had satisfactory imaging and were included in the present analysis. At baseline, median hematoma volume for all patients was 15.6 (19.7) ml and edema volume was 1.65 (3.4) ml. There were no differences between the <150mmHg (n=26) and the <180mmHg (n=27) treatment groups with respect to clinical characteristics, baseline volumes, and time to randomization.

Mean perihematoma PS (5.1±2.4 ml/100ml/min) was elevated relative to contralateral regions (3.6±1.6 ml/100ml/min, P<0.001) as was mean PS in the ipsilateral hemisphere. There was no relationship identified between baseline hematoma volume and hematoma PS or baseline BP and hematomal/peri-hematomal PS. Mean PS was similar in the two BP groups at 2 hours post randomization. Acute hematoma volume predicted absolute peri hematoma edema volume at baseline and the change in absolute edema volume over24h was also predicted by acute hematoma volume. Modest focal increases in BBB permeability were found which did not impact edema growth. 

What are the major take home points from this study? Does it change our clinical practice? The sample size is too small to conclude one way or the other. However, it is interesting to note that the permeability surface area product or BBB permeability does not seem to be affected by baseline BP or change in BP, nor does it seem to impact hematoma growth. The authors acknowledge that the imaging acquisition was at <24 hours and no conclusions can be drawn about hematoma growth past that time. Additionally, they postulate that the cause of peri-hematomal edema may not vasogenic as only modest focal changes in hematomal and peri-hematomal PS were observed that did increase edema volume. Although this is a novel approach to study permeability of BBB I think it needs further validation in a larger cohort.